This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/AU00/01568 which has an International filing date of Dec. 18, 2000, which designated the United States of America.
The present invention is directed to the area of mechanical continuously variable power transmissions, in particular continuously variable transmission (CVT) systems for vehicles.
There is presently a trend towards the use of CVT systems in automobiles, beginning in the super-mini class and progressing through to mid-size luxury vehicles. There are many advantages to using a CVT system over a conventional manual or automatic transmission, for example, improvements in economy, performance and versatility. Electronic control easily allows the CVT to be switched between automatic operation and a xe2x80x9cmanualxe2x80x9d mode where it can emulate a clutch-less manual transmission on demand. However most of the CVT systems proposed to date have been limited in that they need additional arrangements of gears to provide reverse and neutral functions.
A small number of prior art CVT systems which can continuously vary the output from a range of forward speeds, though zero to reverse ratios have been proposed. These can have additional application in mopeds and motorcycles as they include an integral reverse. They all use twin, parallel power transmission paths, one path including a CVT, to achieve the desired result of a CVT which can continuously vary the output ratio between two opposite directions, passing cleanly through zero. This prior art can be grouped into two basic arrangements. The first arrangement, proposed by Cowan in U.S. Pat. No. 5,121,936 and by Wilkes et al. in WO 98/54489, uses a planetary gear set to combine the output of the parallel transmission paths of the CVT and another direct or geared drive, such that the final output may vary continuously through a range of forward speeds, zero, and reverse. The second arrangement, proposed by Suzuki in JP 10-274293 and Kanetani JP 8-61459 utilises a differential to combine the CVT path and the linear power transmission path to achieve the same result of a CVT which can continuously vary the output ratio between two opposite directions, passing cleanly through zero. All of these arrangements can be quite bulky and involve more complexity and parts as they use planetary gear-sets or differentials in addition to a CVT.
It is therefore the object of the present invention to provide a continuously variable reversible transmission (CVRT) which overcomes some or all of the disadvantages of the prior art, namely complexity and package size.
With this object in view, there is provided by the present invention a continuously variable reversible transmission system including an input shaft, a housing, an input arm, first and second CVT shafts, a fixed input wheel, a ratio selector mechanism, an overall output wheel and an output shaft. The input shaft has a major axis and the input arm may be fixed to the input shaft, the input arm may include at least first and second portions, each input arm portion extending substantially perpendicular to the input shaft. At each end of the input arm first and second portions, a respective first and second CVT shaft may be rotatably mounted, each of the first and second CVT shafts having a respective major axis extending substantially parallel to the input shaft, the major axis of each of the respective first and second CVT shafts being the axis of rotation of the respective shaft with respect to the input arm.
The fixed input wheel may be aligned with the major axis of the input shaft, the first CVT shaft may be coupled with the fixed input wheel, the second CVT shaft may be coupled with the first CVT shaft, the overall output wheel may be coupled with the second CVT shaft, and the overall output wheel may be fixed to the output shaft. In this arrangement, the first and second CVT shafts may orbit around the major axis of the input shaft due to rotation of the input shaft, such that changing a ratio of at least one of the couplings produces a variation of the speed of the output shaft from forwards, through zero to reverse.
The continuously variable reversible transmission may include a CVT sub-assembly which rotates about the major axis of the input shaft, the CVT sub-assembly including the input arm, the first and second CVT shafts, a CVT input wheel and a CVT output wheel. The CVT input wheel may be mounted on the first CVT shaft such that relative rotation of the CVT input wheel and the first CVT shaft is prevented. The CVT output wheel being mounted on the second CVT shaft such that relative rotation of the CVT output wheel and the second CVT shaft is prevented. The coupling of the first CVT shaft with the fixed input wheel may include the CVT input wheel, and the coupling of the second CVT shaft with the overall output wheel including the CVT output wheel. The rotation of the CVT sub-assembly may thereby cause rotation of the CVT input wheel relative to the fixed input wheel, resulting in a rotation of the first CVT shaft about its major axis in addition to its orbit about the major axis of the input shaft. The coupling between the first CVT shaft and the second CVT shaft in the CVT sub-assembly may be arranged to permit a variable rotation of the second CVT shaft relative to the first CVT shaft, producing a variable CVT ratio. The variable rotation of the second CVT shaft and the CVT output wheel about the major axis of the second shaft in addition to the orbit of the second shaft about the major axis of the input shaft may thereby cause a rotation of the overall output wheel due to the coupling between the CVT output wheel and the overall output wheel, the overall output wheel being fixed to the output shaft. The rotation of the output shaft may then be zero when the CVT ratio is of a set magnitude. As the CVT ratio is increased above the set magnitude, the output shaft turns in a forward direction and as the CVT ratio is decreased below the set magnitude, the output shaft turns in a reverse direction.
The set magnitude of the CVT ratio required to produce zero rotation of the output shaft may be calculated from the effective pitch circle diameters of at least the CVT input wheel, the CVT output wheel and the overall output wheel. As the transmission system is a planetary arrangement, the sizes of the components are all interrelated. Other dimensions can therefore be substituted to enable the same calculation using different combinations of dimensions.
The fixed input wheel and the CVT input wheel may both be toothed gear wheels. The fixed input wheel may be an external tooth gear wheel, like a sun gear in a conventional planetary gear system. Alternatively, the fixed input wheel may be an internally toothed gear wheel meshing with the CVT input wheel like a ring gear in a planetary gear system.
Alternatively the coupling between the fixed input wheel and the CVT input wheel may be achieved by using a looped link, such as a belt, chain or other form of segmented strap. If the fixed input wheel and the CVT input wheel are pulley wheels, then the looped link may be a belt. If these pulley wheels are of variable width, the pulley wheels and belt may thereby provide a variable ratio of the coupling between the fixed input wheel and the CVT input wheel. However, in yet another possible alternative, the looped link may be a chain.
Similarly, on the output side, the overall output wheel and the CVT input wheel may both be toothed gear wheels. The overall output wheel may be an external tooth gear wheel like a sun gear in a conventional planetary gear system. Alternatively, the overall output wheel may be an internally toothed gear wheel meshing with the CVT output wheel like a ring gear in a planetary gear system.
The coupling between the overall output wheel and the CVT output wheel may be by a looped link which can be any belt or chain type device, for example it may be a segmented strap. If the overall output wheel and the CVT output wheel are pulley wheels then the looped link may be a belt, then if the pulley wheels are of variable width, the pulley wheels and belt may thereby provide a variable ratio of the coupling between the overall output wheel and the CVT output wheel. Alternatively, the looped link may be a chain.
The CVT sub-assembly may include a first and a second pair of variable cone pulley wheels coupled by a pulley belt. The first pair of variable cone pulley wheels may be located on the first CVT shaft such that the space between the pulley wheels can be varied and such that the pulley wheels are driven to rotate with the first CVT shaft, the second pair of variable cone pulley wheels may be located on the second CVT shaft such that the space between the pulley wheels can be varied and such that the pulley wheels are driven to rotate with the second CVT shaft. The pulley belt may run between and engage the first and second pairs of variable cone pulley wheels such that as the spacing between the variable cone pulley wheels of each pair of variable cone pulley wheels is changed in opposing directions, the rotation of the second pair of variable cone pulley wheels is increased or reduced in relation to the rotation of the first pair of variable cone pulley wheels, thereby producing a variable CVT ratio. Additionally, the CVT input wheel may be an integral part of one of the pulley wheels of the first pair of variable cone pulley wheels and/or the CVT output wheel may be an integral part of one of the pulley wheels of the second pair of variable cone pulley wheels.
Alternatively, the CVT sub-assembly may include first and second curved friction discs and at least two friction wheels, a second CVT input wheel and a second CVT output wheel. The first and second curved friction discs may be located along the major axis of the input shaft such that they are free to rotate about said axis. The second CVT input wheel may be fixed to the first CVT shaft and may be coupled to the first curved friction disc, the second CVT output wheel may be fixed to the second CVT shaft and may be coupled to the second curved friction disc. Each of the at least two friction wheels may be in contact with each of the curved friction discs, the contact points between the friction wheels and the curved friction discs being controlled by an angular rotation of the friction wheels about an axis which is substantially perpendicular to the input shaft major axis such that as the contact points are varied along the curve of each curved friction disc by controlling the angular rotation of the friction wheels, the rotational speed of the second curved friction disc is changed in relation to the rotational speed of the first curved friction disc, thereby producing a variable CVT ratio.
Alternatively, two variable ratios may be used in series to increase the range of ratios available from the continuously variable reversible transmission. Respective first and second pulley wheels may be fixedly mounted to the first and second CVT shafts, each of the first and second pulley wheels including at least one angled channel around its periphery. The fixed input wheel may be an external ring including friction nodes which contact the at least one angled channel of the first pulley wheel, the friction nodes being controlled radially to vary the point of contact between the friction nodes and the first pulley wheel, to thereby provide a first variable ratio between the rotational velocity of the input shaft about its major axis and the rotational velocity of the first pulley wheel about the major axis of the first CVT shaft. The first CVT shaft may be coupled with the second CVT shaft by a gear fixedly mounted on each shaft. Alternatively, the gears may be an integral part of each pulley wheel. The coupling may be by a looped link. Similarly, the overall output wheel may be an external ring including friction nodes which contact the at least one angled channel of the second pulley wheel, the friction nodes being controlled radially to vary the point of contact between the friction nodes and the second pulley wheel, to thereby provide a second variable ratio between the rotational velocity of the second pulley wheel about the major axis of the second CVT shaft and about the major axis of the input shaft and the rotational velocity of the overall output wheel about the input shaft major axis. The rotation of the output shaft being zero when the ratio between the first variable ratio and the second variable ratio is of a set magnitude. It may be preferable to use only one variable ratio in this arrangement, for example the second variable ratio may be fixed to eliminate the need for adjusting the position of the friction nodes in the rotating overall output wheel.
As may be appreciated, many combinations of the above arrangements are possible in designing a continuously variable reversible transmission system according to the present invention. For example different input and output arrangements to the CVT may be combined to change the range of ratios available, to vary the position of the zero output position within that range of ratios, and to reverse the output direction as required.
Practical applications of the present invention will now be described by way of examples with reference to the accompanying drawings.